i) Field of the Invention
The present invention relates to novel 2-alkoxy-3,5-diaminopyridine derivatives and their salts, and dye compositions for keratinous fibers which contain the derivatives or salts as a coupler. The present dye compositions impart a bright blue tone with enhanced fastness to keratinous fibers.
ii) Discussion of the Background
Conventionally, keratinous fibers (such as hair) have generally been dyed by so-called oxidation dye compositions, which contain developers and couplers in combination. The dyeing mechanism of the oxidation dyes is primarily based on a chemical oxidation reaction, where a coupling agent is oxidized, and simultaneously, the oxidative coupling of a developer and a coupler firmly dyes the keratinous fiber.
Conventional developers include p-phenylene diamine derivatives, p-aminophenol derivatives, diaminopyridine derivatives, 4-aminopyrazolone derivatives and heterocyclic hydrazone. Conventional couplers include alpha-naphthol, o-cresol, m-cresol, 2,6-dimethylphenol, 2,5-dimethylphenol, 3,4-dimethylphenol, 3,5-dimethylphenol, benzcatechin, pyrogallol, 1,5-dihydroxynaphthalene, 1,7-dihydroxynaphthalene, 5-amino-2-methylphenol, hydroquinone, 2,4-diaminoanisole, m-toluylenediamine, o-aminophenol, resorcin, resorcin monomethyl ether, m-phenylene diamine, 1-phenyl-3-methyl-5-pyrazolone, 1-phenyl-3-amino-5-pyrazolone, 1-phenyl-3,5-diketopyrazolidine, 1-methyl-7-dimethylamino-4-hydroquinolone-2,1-amino-3-acetylacetamino-4-ni trobenzol, 1-amino-3-cyanacetylamino-4-nitrobenzol, m-aminophenol, 4-chlororesorcin, 2-methylresorcin, 2,4-diaminophenoxy ethanol, 2,6-diaminopyridine, 3,5-diaminotrifluoromethylbenzene, 2,4-diaminofluorobenzene, 3,5-diaminofluorobenzene, 2,4-diamino-6-hydroxypyrimidine, 2,4,6-triaminopyrimidine, 2-amino-4,6-dihydroxypyrimidine, 4-amino-2,6-dihydroxypyrimidine and 4,6-diamino-2-hydroxypyrimidine.
Conventional couplers to be incorporated in oxidation dye compositions, however, have provided only insufficient results in terms of color brightness, dyeability and color fastness. Since these properties are greatly influenced by the chemical characteristics of the coupler, it is very important to search for a coupler capable of achieving improved dye properties.
Among the conventional oxidation dye compositions, m-phenylene diamine and 2,6-diaminopyridine provide a blue tone of high brightness. However, the blue tone obtained is easily discolored, the color is quickly washed away by shampooing, and in addition, the color fastness is poor.